Thermally Foamable Microsphere, Method of Producing the Same, and Use Thereof

ABSTRACT

This invention aims to provide a thermally foamable microsphere which is excellent in heat resistance, has a high expansion ratio, and shows stable foaming behavior; a method of producing the thermally foamable microsphere; and suitable use thereof. 
     This invention provides a thermally foamable microsphere in which an outer shell encapsulating a foaming agent is formed of a copolymer having a polymethacrylimide structure. In particular, this invention provides a thermally foamable microsphere in which monomers capable of forming the polymethacrylimide structure by a copolymerization reaction are methacrylonitrile and methacrylic acid. Moreover, this invention provides a method of producing the thermally foamable microsphere and use of the thermally foamable microsphere as an additive.

TECHNICAL FIELD

The present invention relates to a technique on a thermally foamablemicrosphere. More specifically, the present invention relates to: athermally foamable microsphere which is excellent in heat resistance,has a high expansion ratio, and shows stable foaming behavior; a methodof producing the thermally foamable microsphere; and suitable usethereof.

BACKGROUND ART

The “thermally foamable microsphere” also referred to as a thermallyexpandable microcapsule is obtained by microencapsulating a volatilefoaming agent with an outer shell formed of a polymer. In general, whensuspension polymerization with a polymerizable mixture containing apolymerizable monomer and a foaming agent is allowed to proceed in anaqueous dispersion medium, an outer shell is formed in such a manner asto encapsulate the foaming agent.

As the polymer forming the outer shell, a thermoplastic resin with goodgas barrier properties is generally used. The polymer forming the outershell is softened with heat. As the foaming agent, a compound having alow boiling point, such as hydrocarbon, which becomes gas at atemperature equal to or lower than the softening point of the polymerforming the outer shell is generally used.

When the thermally foamable microsphere is heated, the foaming agent isvaporized to generate expanding force acting on the outer shell.Simultaneously, the elastic modulus of the polymer forming the outershell drastically decreases, which causes rapid expansion at a certaincritical temperature. This temperature is referred to as a “foamingstarting temperature.” When the thermally foamable microsphere is heatedto a temperature equal to or higher than the foaming startingtemperature, foamed particles (expanded and closed cells) are formed dueto the expansion phenomenon. When further heated, the foaming agenttransmits the outer shell, which has become thin, resulting in reducedinternal pressure, which causes contraction of the foamed particles(shrinking phenomenon).

Utilizing the above-described properties which allows the formation ofthe foamed particles, the thermally foamable microsphere is applied to awide variety of fields, such as a designability providing agent, afunctionality providing agent, and a weight reducing agent. For example,the thermally foamable microsphere is added to a polymeric material,such as a synthetic resin (a thermoplastic resin and a thermosettingresin) and rubber, a coating composition, ink, etc., for use. Whenhigher performance is required in each field to which the microsphere isapplied, the demand level to the thermally foamable microsphereincreases. Thus, for example, the improvement in the processingproperties, such as heat resistance, is required.

However, in a conventional thermally foamable microsphere, the foamingstarting temperature is generally within a narrow range and foamingstarts at relatively low temperatures. Therefore, the thermally foamablemicrosphere is likely to develop premature foam at the time ofprocessing, such as kneading or pelletization before foamed molding.Therefore, the processing temperatures need to be low, which limits thetype of an applicable synthetic resin or rubber.

Conventionally, in order to obtain a thermally foamable microsphereusable at high temperatures, a thermally foamable microsphere has beenproposed: which each comprises: a shell of a polymer obtained by thepolymerization of acrylonitrile (I) as the main monomer, a monomer (II)having a carboxyl group, and a monomer (III) having a group reactivewith the carboxyl group of the monomer (II); and encapsulated therein aliquid having a boiling point not higher than the softening point of thepolymer (Patent Document 1). The foamed article obtained by the methodhas a feature of having a glass-like fragile outer shell. For thisreason, the foamed article is completely different from one havingelasticity. Thus, the properties of resin may be lost when producing aporous body whose shape varies.

Moreover, Patent Document 2 proposes a method of forming an outer shellresin of a thermally foamable microsphere from a polymer of a monomermixture containing a nitril monomer (I), a monomer (II) having oneunsaturated double bond and a carboxyl group in the molecule, a monomer(III) having two or more polymerizable double bonds in the molecule,and, as required, a monomer (IV) which can be copolymerized with themonomers. According to this method, the heat resistance can beincreased. However, by the use of a monomer having two or morepolymerizable double bonds in the molecule, a polymer takes a crosslinkage structure, whereby the expansion ratio is suppressed. Whenacrylonitrile is used in a high proportion, aggregation occurs to form alump in the middle of polymerization, which makes it difficult to securemanufacturability. Moreover, when acrylonitrile is used in a highproportion, yellowing is remarkable on heating.

Conventionally, polymethacrylimide is known as a polymeric materialhaving high heat resistance, and a polyimide foam substance using suchmaterial is disclosed in Patent Document 3. The production methoddisclosed in Patent Document 3 refers to a method of heating and foaminga polymer plate after producing a foam substance, and does not refer toa method of producing a thermally foamable microsphere.

Patent Document 1: International Publication WO 99/43758 Patent Document2: International Publication WO 03/099955 Patent Document 3: JapaneseLaid-open Publication No. 10-306169 DISCLOSURE OF THE INVENTIONTechnical Problems to be Solved

A main object of the present invention is to provide a thermallyfoamable microsphere which is excellent in heat resistance, has a highexpansion ratio, and shows stable foaming behavior; a method ofproducing the thermally foamable microsphere; and suitable use thereof.

Means to Solve the Problems

In order to achieve the object, the present inventors conductedextensive research, and, as a result, found that by forming a copolymercapable of forming a polymethacrylimide structure into an outer shell, athermally foamable microsphere which is excellent in heat resistance,has a high expansion ratio, and shows stable foaming behavior can beobtained.

Thus, in the present invention, the outer shell encapsulating thefoaming agent first provides a thermally foamable microsphere capable offorming a copolymer having a polymethacrylimide (abbreviated as PMI)structure. More specifically, the thermally foamable microsphere of thepresent invention contains a foaming agent and an outer shellencapsulating the foaming agent thereinside; and has a structure capableof being formed by a copolymer in which the outer shell has thepolymethacrylimide structure. As a suitable example of the monomercapable of forming the polymethacrylimide structure due to acopolymerization reaction, methacrylonitrile and methacrylic acid arementioned.

The thermally foamable microsphere of the present invention has featuresthat the b* value after heated at 240° C. for 2 minutes is 100 or lowerand that the variations in the foaming starting temperature and themaximum foaming temperature due to heat treatment at temperatures lowerthan the foaming starting temperature are 7% or lower relative to thefoaming starting temperature and the maximum foaming temperature beforethe heat treatment, respectively.

Next, the present invention provides a method of producing a thermallyfoamable microsphere in which a foaming agent is encapsulated in theouter shell capable of forming a copolymer having the polymethacrylimidestructure by performing suspension polymerization of a mixture ofmonomers as main components comprised of a nitril monomer and a monomerhaving a carboxyl group in an aqueous dispersion medium containing adispersion stabilizer in the presence of the foaming agent.

In the production method, methacrylonitrile can be used as the nitrilmonomer and methacrylic acid can be used as the monomer having acarboxyl group. More specifically, the mixture of a polymerizablemonomer is designed to contain at least: a substance in which the molarratio of methacrylonitrile to methacrylic acid is 1:9 to 9:1 in aproportion of 70 to 100% by weight; a vinyl monomer capable of beingcopolymerized therewith in a proportion of 0 to 30% by weight; and across-linkable monomer having two or more functionalities in aproportion of 0 to 0.4 mol %, and more preferably 0 to 0.3 mol %.

Furthermore, the present invention provides use of the above-describedthermally foamable microsphere as an additive. The thermally foamablemicrosphere of the present invention has features that the foamingstarting temperature can be sufficiently raised. Therefore, undesirablepremature foaming can be effectively suppressed when heated to hightemperatures at the time of mixing with various synthetic resins,rubber, and a binder resin. Moreover, even after heated, the thermallyfoamable microsphere of the present invention shows maintained stablefoaming behavior; has high expansion ratio; and shows less shrinking.Therefore, the addition amount thereof can be reduced and a broadprocessing window can be achieved.

EFFECT OF THE INVENTION

The present invention can provide a thermally foamable microsphere whichis excellent in heat resistance, has a high expansion ratio, and shows astable foaming behavior. Moreover, the present invention can provide athermally foamable microsphere whose processing temperature beforefoaming can be increased, and, in addition thereto, whose foamingstarting temperature does not lower even after heat treated.

Furthermore, the present invention can provide a thermally foamablemicrosphere with little yellowing at the time of heating. Moreover, thepresent invention can stably produce a thermally foamable microspherewhile causing no aggregation in the middle of polymerization.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, embodiments of the present invention will be described. Thescope of the present invention is not narrowly limited by Embodiments orExamples which will be described below.

A thermally foamable microsphere of the present invention has featuresof containing a foaming agent and an outer shell encapsulating thefoaming agent thereinside, in which the outer shell has a structurecapable of foaming a copolymer having a polymethacrylimide structure.

The “polymethacrylimide structure” can be obtained by cyclizing anitrile group and a carboxyl group by heating or the like. Thus, as amonomer for forming the outer shell, a nitril monomer and a monomerhaving a carboxyl group are main components.

As the “nitril monomer”, methacrylonitrile is used as a main componentand, as required, acrylonitrile, α-chloroacrylonitrile,α-ethoxyacrylonitrile, fumaronitrile, etc., may be used together.

As the “monomer having a carboxyl group”, methacrylic acid is used as amain component and, as required, acrylic acid, itaconic acid, crotonicacid, maleic acid, maleic anhydride, fumaric acid, citraconic acid,etc., may be used together.

The molar ratio of methacrylonitrile to methacrylic acid is 1:9 to 9:1,more preferably 1:5 to 5:1, and still more preferably 1:3 to 3:1.Besides methacrylonitrile and methacrylic acid, a vinyl monomer capableof copolymerized therewith may be used. These substances are used foradjusting the foaming properties of a polymer of the outer shell. Whenthe molar ratio of methacrylonitrile to methacrylic acid is lower than1:9, the particle formation ability is lowered, agglomeration occursduring polymerization, and while the molar ratio of methacrylonitrile tomethacrylic acid exceeds 9:1, yellowing on heating is remarkable and theheat resistance is deteriorated.

Mentioned as the “vinyl monomer” are: vinylidene chloride; vinylacetate; (meth)acrylic acid ester, such as methyl(meth)acrylate,ethyl(meth)acrylate, n-butyl(meth)acrylate, isobutyl(meth)acrylate,t-butyl(meth)acrylate, isobornyl(meth)acrylate,cyclohexyl(meth)acrylate, benzyl(meth)acrylate, and β-carboxy ethylacrylate; styrene monomers, such as styrene, styrene sulfonic acid orsodium salts thereof, α-methyl styrene, and chlorostyrene; monomers inwhich a polymerization reaction proceeds by a radical initiator, such asacrylamide, substituted acrylamide, methacrylamide, and substitutedmethacrylamide; and mixtures thereof. The above-mentionedcopolymerizable vinyl monomers can be used in a proportion of about 0 to30% by weight. When the vinyl monomer exceeds 30% by weight, the effectof polymethacrylimide decreases.

In the present invention, a polymethacrylimide structure is formedthrough the cyclization of a nitrile group and a carboxyl group.Therefore, the use of a cross-linkable monomer is not essential.However, when using a cross-linkable monomer, a polyfunctional monomerhaving two or more polymerizable carbon-carbon double bonds (—C═C—) ispreferable. As the polymerizable carbon-carbon double bond, a vinylgroup, a methacrylic group, an acrylic group, and an allyl group arementioned. The two or more polymerizable carbon-carbon double bonds eachmay be the same or different. Or, two or more different cross-linkablemonomers may be used.

Mentioned as a more specific example of the “cross-linkable monomer”are: aromatic divinyl compounds, such as divinylbenzene,divinylnaphthalene, and derivatives thereof; diethylene unsaturatedcarboxylic acid ester, such as ethylene glycol diacrylate, diethyleneglycol diacrylate, ethylene glycol dimethacrylate, and diethylene glycoldimethacrylate; polyethylene unsaturated carboxylic acid ester, such astriethylene glycol diacrylate and triethylene glycol dimethacrylate;acrylate or methacrylate derived from aliphatic terminated alcoholhaving alcoholic groups at both ends, such as 1,4-butanediol and1,9-nonanediol; and a cross-linkable monomer having two functionalitiessuch as a divinyl compound or the like (e.g., N,N-divinylaniline anddivinyl ether). Mentioned as other cross-linkable monomers are, forexample, polyfunctional cross-linkable monomers having three or morefunctionalities, such as trimethylolpropane triacrylate,trimethylolpropane trimethacrylate, pentaerythritol triacrylate,pentaerythritol trimethacrylate, and triacrylformal; and triallylcyanurate or triallyl isocyanurate. A suitable addition amount of thecross linking agent is 0 to 0.4 mol %, and more preferably 0 to 0.3 mol%. When the cross linking agent is used in a proportion exceeding 0.4mol %, the expansion ratio is sharply reduced.

Next, mentioned as the “foaming agent” encapsulated in theabove-mentioned outer shell are: hydrocarbons, such as methane, ethane,propane, n-butane, isobutane, n-pentane, isopentane, neopentane,n-hexane, isohexane, n-heptane, isoheptane, n-octane, isooctane,n-nonane, isononane, n-decane, isodecane, n-dodecane, and isododecane;chlorofluorocarbon, such as CCl3F; tetraalkylsilanes, such astetramethylsilane. These foaming agents can also be used singly or incombination of two or more members in accordance with the object orintended use. Moreover, a chemical foaming agent can also be usedtogether.

The proportion of the foaming agent encapsulated in the thermallyfoamable microsphere is generally 5 to 50% by weight, and preferably 7to 40% by weight based on the total amount. Therefore, it is preferableto adjust the proportion of each of the polymerizable monomer and thefoaming agent in such a manner that the proportion of each of an outershell polymer and the foaming agent is within the above-mentioned rangeafter polymerization.

Hereinafter, a method of producing the thermally foamable microsphere ofthe present invention will be described.

First, the thermally foamable microsphere having the above-mentionedstructure can be generally produced by performing suspensionpolymerization of a polymerizable mixture in an aqueous dispersionmedium containing a dispersion stabilizer in the presence of a foamingagent.

More specifically, a polymerizable monomer mixture containing at least apolymerizable monomer and a foaming agent is dispersed in an aqueousdispersion medium to thereby form a droplet of an oil-basedpolymerizable monomer. This process may be referred to as a “particleformation process.”

In the particle formation process of the present invention, thepolymerizable monomer mixture capable of forming a polymethacrylimidestructure and an aqueous dispersion medium are stirred and mixed tothereby form a droplet of the polymerizable monomer mixture in theaqueous dispersion medium.

It is preferable to adjust the average particle diameter of the dropletto be substantially the same as the average particle diameter of thetarget thermally foamable microsphere. The average particle diameter ofthe droplet is generally 1 to 500 μm, preferably 3 to 300 μm, andparticularly preferably 5 to 200 μm.

In order to obtain a thermally foamable microsphere having an extremelysharp particle size distribution, it is preferable to employ a methodwhich involves: supplying an aqueous dispersion medium and apolymerizable monomer mixture into a continuous high speed high-sheartype stirring and dispersing machine; successively stirring both of themin the stirring dispersion apparatus for dispersion; pouring theobtained dispersion into a polymerization tank; and performingsuspension polymerization in the polymerization tank.

When suspension polymerization of the polymerizable monomer is performedusing a polymerizable initiator following the droplet formation, athermally foamable microsphere having a structure in which the foamingagent is encapsulated in the outer shell formed of a produced polymercan be obtained through the suspension polymerization.

The “suspension polymerization” is generally performed by degassing theinside of the reaction chamber or replacing the inside of the reactionchamber with inert gas, and then increasing the temperature to 30 to100° C. During the suspension polymerization, the polymerizationtemperature may be controlled to a fixed temperature or may be graduallyincreased for polymerization. After the suspension polymerization, thereaction mixture containing the generated thermally foamable microsphereis subjected to filtration, centrifugal separation, sedimentation or thelike, to thereby isolate the thermally foamable microsphere from thereaction mixture. The isolated thermally foamable microsphere is washedand filtered, and then collected in the state of a wet cake. The surfaceof the thermally foamable microsphere can also be coated with variousmaterials as required.

As a “polymerization initiator” for suspension polymerization,polymerization initiators, which are generally used in this technicalfield, can be used. An oil soluble polymerization initiator which issoluble in the polymerizable monomer is preferable. Mentioned as such apolymerization initiator are, for example, hyperoxidation dialkyl,hyperoxidation diacyl, peroxy ester, peroxy dicarbonate, and azocompounds.

More specific examples of the polymerization initiator include: dialkylperoxide, such as methylethyl peroxide, di-t-butyl peroxide, and dicumylperoxide; diacyl peroxide, such as isobutyl peroxide, benzoyl peroxide,2,4-dichlorobenzyl peroxide, 3,5,5-trimethylhexanoyl peroxide; peroxyester, such as t-butyl peroxypivalate, t-hexyl peroxypivalate, t-butylperoxyneodecanoate, t-hexyl peroxyneodecanoate,1-cyclohexyl-1-methylethyl peroxyneodecanoate, 1,1,3,3-tetramethylbutylperoxyneodecanoate, cumil peroxyneodecanoate, and(α,α-bis-neodecanolyperoxy)diisopropylbenzene; peroxydicarbonate, suchas bis(4-t-butylcyclohexyl)peroxydicarbonate,di-n-propyl-oxydicarbonate, diisopropyl peroxydicarbonate,di(2-ethylethylperoxy)dicarbonate, dimethoxy butyl peroxydicarbonate,di(3-methyl-3-methoxybutylperoxy)dicarbonate; azo compounds, such as2,2′-azobisisobutyronitrile,2,2′-azobis(4-methoxy)-2,4-dimethylvaleronitrile,2,2′-azobis(2,4-dimethylvaleronitrile), and1,1′-azobis(1-cyclohexanecarbonitrile); etc.

The polymerization initiator is generally blended in the polymerizablemonomer mixture. However, when premature polymerization needs to besuppressed, a part or the whole of the polymerization initiator may beadded to the aqueous dispersion medium during or after the particleformation process to thereby transfer the polymerization initiator intothe droplet of the polymerizable monomer mixture. The polymerizationinitiator is generally used in a proportion of 0.0001 to 3% by weightbased on the weight of the polymerizable monomer.

The suspension polymerization is generally performed in the aqueousdispersion medium containing a dispersion stabilizer. As the dispersionstabilizer, inorganic particles, such as silica and magnesium hydroxide,can be mentioned, for example. As an auxiliary stabilizer, acondensation product of diethanolamine and an aliphatic dicarboxylicacid, polyvinyl pyrrolidone, polyethylene oxide, various emulsifiers,etc. can be used, for example. The dispersion stabilizer is generallyused in a proportion of 0.1 to 20 parts by weight based on 100 parts byweight of the polymerizable monomer.

The aqueous dispersion medium containing the dispersion stabilizer isgenerally prepared by blending a dispersion stabilizer and an auxiliarystabilizer to deionized water. The pH of the aqueous phase at the timeof polymerization is suitably determined depending on the type of thedispersion stabilizer or auxiliary stabilizer to be used. For example,when silica, such as colloidal silica, is used as the dispersionstabilizer, polymerization is performed in an acid environment. An acidaqueous dispersion medium is obtained by adding acid, as required, tothe aqueous dispersion medium to thereby adjust the pH of the reactionsystem to 6 or lower, and preferably about 3 to 4. In the case of thedispersion stabilizer which dissolves in the aqueous dispersion mediumin an acid environment, such as magnesium hydroxide and calciumphosphate, polymerization is performed in an alkaline environment.

As one of suitable possible combinations of the dispersion stabilizers,combination of colloidal silica and a condensation product is mentioned.As the condensation product, a condensation product of diethanolamineand an aliphatic dicarboxylic acid is preferable. In particular, acondensate of diethanolamine and adipic acid and a condensation productof diethanolamine and itaconic acid are preferable. The acid value ofthe condensation product is preferably 60 or higher and lower than 95,and more preferably 65 to 90.

Furthermore, when mineral salt, such as sodium chloride and sodiumsulfate, is added, a thermally foamable microsphere having a moreuniform particle shape is likely to be obtained. As the mineral salt,salt is generally preferable.

The used amount of the above-mentioned colloidal silica changesdepending on the particle diameter, and is generally 0.5 to 20 parts byweight, and preferably 1 to 15 parts by weight based on 100 parts byweight of the polymerizable monomer. The condensation product is usedgenerally in a proportion of 0.05 to 2 parts by weight based on 100parts by weight of the polymerizable monomer. The mineral salt is usedin a proportion of 0 to 100 parts by weight based on 100 parts by weightof the polymerizable monomer.

As one of other preferable possible combinations of dispersionstabilizers, combination of colloidal silica and a water-solublenitrogen containing substance is mentioned. Among such combinations,combination of colloidal silica and polyvinyl pyrrolidone is preferablyused. Furthermore, as other preferable possible combinations,combination of magnesium hydroxide and/or calcium phosphate and anemulsifier is mentioned.

As the “dispersion stabilizer”, colloid of a metal hydroxide which ishard to dissolve in water (e.g., magnesium hydroxide) obtained by areaction, in the aqueous phase, of a water-soluble polyvalent metal saltcompound (e.g., magnesium chloride) with alkali metal hydroxide (e.g.,sodium hydroxide) can be used. As calcium phosphate, a reaction productin the aqueous phase of sodium phosphate and calcium chloride can beused.

Although an “emulsifier” is not generally used, but, as desired, anionicsurfactants, such as dialkyl sulfosuccinate and phosphoric acid ester ofpolyoxyethylene alkyl(allyl)ether may be used.

As a “polymerization aid”, at least one type of compound selected fromthe group consisting of alkali metal nitrite, stannous chloride, stannicchloride, water-soluble ascorbic acids, and boric acids can be made toexist in the aqueous dispersion medium. When suspension polymerizationis performed in the presence of the above-mentioned compounds,aggregation of polymerization particles does not occur and thepolymerized substance does not attach to the wall of a polymerization atthe time of polymerization, whereby a thermally foamable microsphere canbe stably produced while efficiently removing heat caused bypolymerization.

Among alkali metal nitrites, sodium nitrite and potassium nitrite arepreferable in terms of the ease of availability and price. As theascorbic acids, ascorbic acid, metal salt of ascorbic acid, ester ofascorbic acid, etc., are mentioned, and water-soluble ascorbic acids arepreferably used among the above. Here, the water-soluble ascorbic acidsrefer to water-soluble ascorbic acids whose solubility in 230° C. wateris 1 g/100 cm³ or higher. Among the above, L-ascorbic acid (vitamin C),sodium ascorbate, and potassium ascorbate are particularly preferablyused in terms of the ease of availability, price, and an operationeffect.

The polymerization assistant containing one or more of theabove-mentioned compounds is used in a proportion of generally 0.001 to1 part by weight, and preferably 0.01 to 0.5 part by weight based on 100parts by weight of the polymerizable monomer.

The order of adding each of the above-mentioned components to theaqueous dispersion medium is suitably determined. In general, water andthe dispersion stabilizer, and, as required, the stabilizer assistant,the polymerization assistant, etc., are added to thereby prepare theaqueous dispersion medium containing the dispersion stabilizer.

The foaming agent, polymerizable monomer (vinyl monomer), andcross-linkable monomer may be separately added to the aqueous dispersionmedium and unified in the aqueous dispersion medium to form apolymerizable monomer mixture (oil-based mixture). In general, thefoaming agent, polymerizable monomer (vinyl monomer), and cross-linkablemonomer are mixed beforehand, and then the mixture is added to theaqueous dispersion medium. The polymerization initiator can be addedbeforehand to the polymerizable monomer for use.

When premature polymerization needs to be avoided, for example, thepolymerizable monomer mixture may be added to the aqueous dispersionmedium, and then the polymerization initiator may be added understirring to be unified in the aqueous dispersion medium. Thepolymerizable monomer mixture and the aqueous dispersion medium may bemixed in another container, mixed and stirred with a stirrer or adisperser having high shearing force, and then charged in apolymerization can.

The thermally foamable microsphere obtained by the above-describedproduction method has a structure in which the foaming agent isencapsulated in the outer shell formed of a polymer and the outer shellhas a polymethacrylimide structure. This polymethacrylimide structure isacquired by cyclizing a nitrile group and a carboxyl group under heat orthe like.

However, there may arise a problem with yellowing and coloring at thetime of heating. The problem is caused by thermal denaturation of anitrile group. Therefore, in order to improve heat yellowing resistance,it is preferable to increase the molar ratio of a carboxyl group.

As an index showing a yellowing degree, a “b* value” in the L*a*b* colorsystem is used. When the b* value is higher, the yellowing degreeincreases, and when the b* value is lower, blue color tone becomesstrong. For example, when the thermally foamable microsphere is used forreducing the weight of a sole of a shoe, a titanium oxide is used for awhite sole. When yellowing is remarkable, a large amount of titaniumoxide needs to be used. Thus, the b* value is 100 or lower, and morepreferably 50 or lower.

The softening temperature of the outer shell resin can be adjusted bychanging the proportion of methacrylonitrile and methacrylic acid. Whenthe softening temperature needs to be lowered, the proportion ofmethacrylonitrile is increased, while when the softening temperatureneeds to be increased, the proportion of methacrylic acid is increased.By changing the softening temperature of the outer shell resin, itbecomes possible to suitably adjust the foaming starting temperature.

As a method of adjusting the expanding starting temperature, it is alsoeffective to change the type of foaming agent. The expanding startingtemperature can also be increased by increasing the proportion of thefoaming agent having a high boiling point. When an outer shell resin ofa conventional thermally foamable microsphere is heated at temperaturesslightly lower than the expanding starting temperature, the expandingstarting temperature is lowered. However, the outer shell resin of thethermally foamable microsphere of the present invention has featuresthat, when heated at temperatures slightly lower than the expandingstarting temperature, the expanding starting temperature is not loweredand the foaming behavior is stable. More specifically, the variations inthe expanding starting temperature and the maximum expansion temperatureby heat treatment at temperatures lower than the expanding startingtemperature are 7% or lower relative to the expanding startingtemperature and the maximum expansion temperature before the heattreatment, respectively. Furthermore, the variations are preferably 5%or lower, and more preferably 3% or lower.

Here, the use of the thermally foamable microsphere of the presentinvention is not limited narrowly. The thermally foamable microsphere ofthe present invention is used in various fields after it is foamed(expanded) or as it is kept unfoamed. For example, making good use ofits expandability, the thermally foamable microsphere of the presentinvention is used as a filler for a paint for automobiles and the like,a foaming agent for wallpaper or foaming ink (for applying reliefpatterns to T-shirt and the like), a shrink-preventing agents, etc. Inparticular, the present invention contributes to reducing the weight ofinterior members or tires of automobiles.

Moreover, utilizing the volume increase caused by foaming, the thermallyfoamable microsphere of the present invention is used as an additive forthe purpose of reducing the weight of polymeric materials such as asynthetic resin (thermoplastic resin, thermosetting resin) and rubber, apaint and various materials making them porous and imparting variousfunctionalities (e.g., slipping properties, heat insulation properties,cushioning properties, sound insulation properties, etc.). As thepolymeric material, polyethylene, polypropylene, polystyrene, ABS resin,SBS, SIS, hydrogenated SIS, natural rubber, various synthetic rubbers,thermoplastic polyurethane, etc., are mentioned.

Furthermore, the thermally foamable microsphere of the present inventioncan be suitably used for the fields of a coating composition, wallpaper,and ink, which are requiring surfaceness and smoothness. The thermallyfoamable microsphere of the present invention is excellent inprocessability, and therefore can be suitably used for the fieldsrequiring processing, such as kneading, calendering, extruding, andinjection molding.

Thus, the thermally foamable microsphere of the present invention can beused as a foaming agent or can be mixed with a polymeric material toform a composition. Or, the thermally foamable microsphere of thepresent invention can be molten and kneaded, while not foamed, with athermoplastic resin to be pelletized, and further can be blended in apolymeric material, a coating composition, ink, etc., and foamed underheat to form articles containing foamed particles (e.g., a foamingmolded article, a foamed coating film, foamed ink).

EXAMPLES

Hereinafter, the present invention will be described with reference toExamples and Comparative Examples. First, the “measurement method” ofeach parameter will be described.

(1) Expanding Starting Temperature and Maximum Expansion TemperatureUsing the TMA-7 model manufactured by PerkinElmer, Inc., “TMAmeasurement” was performed. About 0.25 mg of a sample was used, and thetemperature was increased at a temperature increase rate of 5°C./minute. Then, the foaming behavior was observed. More specifically, asample (thermally foamable microsphere) was put in a container, and thetemperature was increased at a temperature increase rate of 5°C./minute. Then, the variation in the height was successively measured.The temperature at which the variation in the height of the sample inthe container started was defined as a expanding starting temperature(Tstart) and the temperature at which the height became a maximum wasdefined as a maximum expansion temperature (Tmax).

(2) Expansion Ratio (Film Coating Method)

To an EVA aqueous emulsion (Concentration: 55% by weight) containingethylene-vinylacetate copolymer (EVA; ethylene/vinyl acetate=30/70% byweight), the thermally foamable microsphere was added in such a mannerthat the ratio of the thermally foamable microsphere to the EVA aqueousemulsion was 5:1 in terms of solid content to prepare a coating liquid.The coating liquid was applied to a double-sided art paper by a coaterhaving a gap of 200 μm, and then the resulting product was put in anoven to dry at 90° C. for 5 minutes. The thickness of the coating filmafter drying was measured. Then, the coating film was put in an ovenhaving a given temperature to heat for 2 minutes for foaming. Thethickness of the coating film after foaming was measured, and then theexpansion ratio was determined from the coating-film pressure ratiobefore and after foaming.

(3) Average Particle Diameter

The average particle diameter was measured using a particle sizedistribution meter SALD-3000J manufactured by Shimadzu Corp.

(4) Measurement of Color Tone

The b* value of the coating film, whose expansion ratio (Film coatingmethod) was measured, was measured using a color difference meter (Colordifference meter CR-200, manufactured by Minolta Co., Ltd.). The b*value refers to a b* value of the L*a*b* color system. When the b* valueis larger, yellow color tone is strong.

(5) Foamed Particle Density

0.5 g of microsphere and 2.5 g of silicon oil were weighed out and putin an aluminum cup. After sufficiently mixing, the mixture was foamedunder heat in an oven having a given temperature, and then the resultantwas taken out. Then, the resultant was put in a 50 ml volumetric flask,and isopropanol was added. Then, the true specific gravity of the foamedmicrosphere was determined from the sample weight and the flask weightafter the addition of isopropanol.

Example 1 (A) Preparation of Aqueous Dispersion Medium

40 g of 20% by weight colloidal silica, 1.6 g of 50% by weightdiethanolamine-adipic acid condensation product (Acid value=78 mgKOH/g),0.12 g of sodium nitrite, 177 g of sodium chloride, and 565 g of waterwere mixed. Then, hydrochloric acid was added so that the pH wasadjusted to 3.2 to thereby prepare an aqueous dispersion medium.

(B) Preparation of Polymerizable Mixture

88 g of methacrylonitrile, which is a polymerization monomer (indicatedas MAN in Tables), 112 g of methacrylic acid (similarly indicated as MAAin Tables), 60 g of isooctane as a foaming agent, and 2 g of2,2′-azobisisobutyronitril (similarly indicated as V-60 in Tables) as apolymerization initiator were mixed to prepare a polymerizable mixture.In Example 1, the molar ratio of methacrylonitrile to methacrylic acidwas 1:1 (see Table 1).

(C) Suspension Polymerization

The aqueous dispersion medium and the polymerizable mixture preparedabove were mixed by stirring with a homogenizer to thereby form a minutedroplet of the polymerizable monomer mixture in the aqueous dispersionmedium. The aqueous dispersion medium containing the minute droplet ofthe polymerizable mixture was charged in a polymerization can with astirrer (1.5 L), heated at 60° C. for 15 hours using a hot water bath,and further heated at 70° C. for 9 hours for reaction. Afterpolymerization, a slurry containing the generated thermally foamablemicrosphere was filtered and washed with water, and dried to therebyobtain a thermally foamable microsphere having an average particlediameter of 40 μm (see Table 1).

(D) Evaluation of Foaming Ability

The TMA measurement was performed using, as a sample, the thermallyfoamable microsphere obtained above as it was. As a result, theexpanding starting temperature was 195° C., the maximum expansiontemperature was 217° C., and the difference therebetween was 22° C. Thethermally foamable microsphere was heated at 170° C. for 2 minutes, andthen the TMA measurement was performed. No changes in both the expandingstarting temperature and the maximum expansion temperature wereobserved. The expansion ratio was 8.4 times at 230° C. (see Table 1).

(E) Measurement of Color Tone

The b* value of the coating film which was heated at 240° C. for 2minutes to foam in (D) above was 24.5 (see Table 1).

Example 2

Suspension polymerization was performed in the same manner with Example1 except using 110 g of methacrylonitrile and 90 g of methacrylic acidto thereby obtain a thermally foamable microsphere with an averageparticle diameter of 39 μm. In Example 2, the molar ratio ofmethacrylonitrile to methacrylic acid was 1.6:1.

The TMA measurement was performed using, as a sample, the thermallyfoamable microsphere obtained as a result of the above manner as it was.As a result, the expanding starting temperature was 186° C., the maximumexpansion temperature was 214° C., and the difference therebetween was28° C. The expansion ratio was 8.4 times at 230° C. and the b* value was26.8.

Example 3

Suspension polymerization was performed in the same manner with Example1 except using 132 g of methacrylonitrile and 68 g of methacrylic acidto thereby obtain a thermally foamable microsphere with an averageparticle diameter of 41 μm. In Example 3, the molar ratio ofmethacrylonitrile to methacrylic acid was 2.5:1.

The TMA measurement was performed using, as a sample, the thermallyfoamable microsphere obtained as a result of the above manner as it was.As a result, the expanding starting temperature was 171° C., the maximumexpansion temperature was 255° C., and the difference therebetween was84° C. The expansion ratio was 10.5 times at 220° C. and the b* valuewas 27.1.

Example 4

Suspension polymerization was performed in the same manner with Example1 except using 154 g of methacrylonitrile and 46 g of methacrylic acidto thereby obtain a thermally foamable microsphere with an averageparticle diameter of 50 μm. In Example 4, the molar ratio ofmethacrylonitrile to methacrylic acid was 4.3:1.

The TMA measurement was performed using, as a sample, the thermallyfoamable microsphere obtained as a result of the above manner as it was.As a result, the expanding starting temperature was 180° C., the maximumexpansion temperature was 260° C., and the difference therebetween was80° C. The expansion ratio was 8.6 times at 220° C. and the b* value was35.4.

Example 5

Suspension polymerization was performed in the same manner with Example1 except using 60 g of isopentane in place of 60 g of isooctane as thefoaming agent to thereby obtain a thermally foamable microsphere with anaverage particle diameter of 40 μm.

The TMA measurement was performed using, as a sample, the thermallyfoamable microsphere obtained as a result of the above manner as it was.As a result, the expanding starting temperature was 185° C., the maximumexpansion temperature was 240° C., and the difference therebetween was55° C. The expansion ratio was 4.5 times at 230° C. and the b* value was25.0.

Example 6

Suspension polymerization was performed in the same manner with Example2 except using 60 g of isopentane in place of 60 g of isooctane as thefoaming agent to thereby obtain a thermally foamable microsphere with anaverage particle diameter of 49 μm.

The TMA measurement was performed using, as a sample, the thermallyfoamable microsphere obtained as a result of the above manner as it was.As a result, the expanding starting temperature was 170° C., the maximumexpansion temperature was 240° C., and the difference therebetween was70° C. The expansion ratio was 9.1 times at 220° C. and the b* value was27.0.

Example 7

Suspension polymerization was performed in the same manner with Example3 except using 60 g of isopentane in place of 60 g of isooctane as thefoaming agent to thereby obtain a thermally foamable microsphere with anaverage particle diameter of 47 μm.

The TMA measurement was performed using, as a sample, the thermallyfoamable microsphere obtained as a result of the above manner as it was.As a result, the expanding starting temperature was 155° C., the maximumexpansion temperature was 220° C., and the difference therebetween was65° C. The expansion ratio was 19.2 times at 210° C. and the b* valuewas 27.5.

Example 8

Suspension polymerization was performed in the same manner with Example4 except using 60 g of isopentane in place of 60 g of isooctane as thefoaming agent to thereby obtain a thermally foamable microsphere with anaverage particle diameter of 50 μm.

The TMA measurement was performed using, as a sample, the thermallyfoamable microsphere obtained as a result of the above manner as it was.As a result, the expanding starting temperature was 130° C., the maximumexpansion temperature was 210° C., and the difference therebetween was80° C. The expansion ratio was 17.3 times at 200° C. and the b* valuewas 36.0.

Example 9

Suspension polymerization was performed in the same manner with Example3 except using 60 g of isododecane in place of 60 g of isooctane as thefoaming agent to thereby obtain a thermally foamable microsphere with anaverage particle diameter of 31 μm.

The TMA measurement was performed using, as a sample, the thermallyfoamable microsphere obtained as a result of the above manner as it was.As a result, the expanding starting temperature was 251° C., the maximumexpansion temperature was 279° C., and the difference therebetween was28° C. The expansion ratio was 1.5 times at 230° C. and the b* value was28.0.

Example 10

Suspension polymerization was performed in the same manner with Example1 except using 130 g of methacrylonitrile, 66 g of methacrylic acid, and4 g of methyl acrylate (indicated as MA in Tables) in place of 88 g ofmethacrylonitrile and 112 g of methacrylic acid to thereby obtain athermally foamable microsphere with an average particle diameter of 34μm.

The TMA measurement was performed using, as a sample, the thermallyfoamable microsphere obtained as a result of the above manner as it was.As a result, the expanding starting temperature was 171° C., the maximumexpansion temperature was 245° C., and the difference therebetween was74° C. The expansion ratio was 10.0 times at 220° C. and the b* valuewas 27.0.

Example 11

Suspension polymerization was performed in the same manner with Example10 except using 60 g of isopentane in place of 60 g of isooctane as thefoaming agent to thereby obtain a thermally foamable microsphere with anaverage particle diameter of 50 μm.

The TMA measurement was performed using, as a sample, the thermallyfoamable microsphere obtained as a result of the above manner as it was.As a result, the expanding starting temperature was 150° C., the maximumexpansion temperature was 220° C., and the difference therebetween was70° C. The expansion ratio was 19.1 times at 210° C. and the b* valuewas 26.9.

The TMA measurement was performed using, as a sample, the thermallyfoamable microsphere obtained as a result of the above manner as it was.As a result, the expanding starting temperature was 171° C., the maximumexpansion temperature was 250° C. or higher, and the differencetherebetween was 79° C. or higher. The expansion ratio was 10.2 times at220° C. and the b* value was 27.0.

Example 13 (A) Preparation of Aqueous Dispersion Medium

65 g of 20% by weight colloidal silica, 6.5 g of 50% by weightdiethanolamine-adipic acid condensation product (Acid value=78 mgKOH/g),0.24 g of sodium nitrite, 0.04 g of stannous chloride, 177 g of sodiumchloride, and 565 g of water were mixed. Then, hydrochloric acid wasadded so that the pH was adjusted to 3.2 to thereby prepare an aqueousdispersion medium.

(B) Preparation of Polymerizable Mixture

175 g of methacrylonitrile (MAN), which is a polymerization monomer, 25g of methacrylic acid (MAA), 60 g of isooctane as a foaming agent, and 2g of 2,2′-azobisisobutyronitril (V-60) as a polymerization initiatorwere mixed to prepare a polymerizable mixture. In Example 13, the molarratio of methacrylonitrile to methacrylic acid was 9:1.

(C) Suspension Polymerization was Performed in the Same manner withExample 1 to thereby obtain a thermally foamable microsphere with anaverage particle diameter of 27 μm.

The evaluation of foaming ability (D) and measurement of color tone (E)were performed using, as a sample, the obtained thermally foamablemicrosphere as it was in the same manner with Example 1. As a result,the expanding starting temperature was 211° C., the maximum expansiontemperature was 218° C., and the difference therebetween was 7° C. Theexpansion ratio was 6.5 times at 220° C. and the b* value was 41.0.

Example 14

Suspension polymerization was performed in the same manner with Example13 except using 129 g of methacrylonitrile and 71 g of methacrylic acidto thereby obtain a thermally foamable microsphere with an averageparticle diameter of 27 μm. In Example 14, the molar ratio ofmethacrylonitrile to methacrylic acid was 2.3:1.

The TMA measurement was performed using, as a sample, the thermallyfoamable microsphere obtained as a result of the above manner as it was.As a result, the expanding starting temperature was 204° C., the maximumexpansion temperature was 259° C., and the difference therebetween was55° C. The expansion ratio was 17.0 times at 230° C. and the b* valuewas 31.0.

Example 15

Suspension polymerization was performed in the same manner with Example13 except using 108 g of methacrylonitrile and 92 g of methacrylic acidto thereby obtain a thermally foamable microsphere with an averageparticle diameter of 26 μm. In Example 15, the molar ratio ofmethacrylonitrile to methacrylic acid was 1.5:1.

The TMA measurement was performed using, as a sample, the thermallyfoamable microsphere obtained as a result of the above manner as it was.As a result, the expanding starting temperature was 189° C., the maximumexpansion temperature was 266° C., and the difference therebetween was77° C. The expansion ratio was 17.6 times at 230° C. and the b* valuewas 27.0.

Moreover, the heat foamed particle density was 0.0046 at 230° C., 0.0045at 240° C., and 0.0068 at 250° C. (see Table 2).

Example 16

Suspension polymerization was performed in the same manner with Example13 except using 88 g of methacrylonitrile and 112 g of methacrylic acidto thereby obtain a thermally foamable microsphere with an averageparticle diameter of 31 μm. In Example 16, the molar ratio ofmethacrylonitrile to methacrylic acid was 1:1.

The TMA measurement was performed using, as a sample, the thermallyfoamable microsphere obtained as a result of the above manner as it was.As a result, the expanding starting temperature was 199° C., the maximumexpansion temperature was 263° C., and the difference therebetween was64° C. The above-mentioned thermally foamable microsphere was heated at180° C. for 10 minutes, and then the TMA measurement was performed.Changes in both the expanding starting temperature and the maximumexpansion temperature were hardly observed. The expansion ratio was 14.5times at 230° C. and the b* value was 24.0.

FIG. 1 shows changes (foaming behavior) in the foaming degree between atthe expanding starting temperature and at the maximum expansiontemperature at the time of TMA measurement. About 0.25 mg of a samplewas put in a container, and the temperature was increased at atemperature increase rate of 5° C./minute. Then, the variation in theheight was successively measured. The height at each temperature wasindicated relative to the height at the maximum expansion temperature(Tmax), which was defined as 1.

As shown in FIG. 1, it is revealed that the thermally foamablemicrosphere obtained in Example 16 hardly shows changes in the expandingstarting temperature and the maximum expansion temperature when notheated and when heated at 180° C. for 10 minutes. In addition, there areno changes in the foaming behavior between at the expanding startingtemperature and at the maximum expansion temperature, and a stablefoaming ability is maintained.

Example 17

Suspension polymerization was performed in the same manner with Example16 except using 60 g of lauryl peroxide (indicated as LPO in Tables)isopentane in place of 2 g of 2,2′-azobisisobutyronitril as thepolymerization initiator to thereby obtain a thermally foamablemicrosphere with an average particle diameter of 30 μm.

The TMA measurement was performed using, as a sample, the thermallyfoamable microsphere obtained as a result of the above manner as it was.As a result, the expanding starting temperature was 200° C., the maximumexpansion temperature was 250° C., and the difference therebetween was50° C. The expansion ratio was 7.1 times at 230° C. and the b* value was23.0.

Example 18

Suspension polymerization was performed in the same manner with Example17 except using 68 g of methacrylonitrile and 132 g of methacrylic acidto thereby obtain a thermally foamable microsphere with an averageparticle diameter of 28 μm. In Example 18, the molar ratio ofmethacrylonitrile to methacrylic acid was 0.7:1.

The TMA measurement was performed using, as a sample, the thermallyfoamable microsphere obtained as a result of the above manner as it was.As a result, the expanding starting temperature was 207° C., the maximumexpansion temperature was 232° C., and the difference therebetween was25° C. The expansion ratio was 4.1 times at 230° C. and the b* value was23.0.

Example 19

Suspension polymerization was performed in the same manner with Example13 except adding, in addition to 175 g of methacrylonitrile and 25 g ofmethacrylic acid, 0.4 g of trimethylolpropanetrimethacrylate (indicatedas TMPTMA in Tables) to thereby obtain a thermally foamable microspherewith an average particle diameter of 30 μm. The blending proportion oftrimethylolpropanetrimethacrylate in the polymerizable monomer mixtureof Example 19 was 0.04 mol %.

The TMA measurement was prepared using, as a sample, the thermallyfoamable microsphere obtained as a result of the above manner as it was.As a result, the expanding starting temperature was 213° C., the maximumexpansion temperature was 218° C., and the difference therebetween was5° C. The expansion ratio was 6.7 times at 230° C.

Example 20

Suspension polymerization was performed in the same manner with Example15 except adding, in addition to 108 g of methacrylonitrile and 92 g ofmethacrylic acid, 0.2 g of trimethylolpropanetrimethacrylate to therebyobtain a thermally foamable microsphere with an average particlediameter of 26 μm. The blending proportion oftrimethylolpropanetrimethacrylate in the polymerizable monomer mixtureof Example 20 was 0.02 mol %.

The TMA measurement was performed using, as a sample, the thermallyfoamable microsphere obtained as a result of the above manner as it was.As a result, the expanding starting temperature was 188° C., the maximumexpansion temperature was 250° C., and the difference therebetween was62° C. The expansion ratio was 10.6 times at 230° C.

Example 21

Suspension polymerization was performed in the same manner with Example15 except adding, in addition to 108 g of methacrylonitrile and 92 g ofmethacrylic acid, 0.6 g of trimethylolpropanetrimethacrylate to therebyobtain a thermally foamable microsphere with an average particlediameter of 29 μm. The blending proportion oftrimethylolpropanetrimethacrylate in the polymerizable monomer mixtureof Example 21 is 0.07 mol %.

The TMA measurement was performed using, as a sample, the thermallyfoamable microsphere obtained as a result of the above manner as it was.As a result, the expanding starting temperature was 187° C., the maximumexpansion temperature was 223° C., and the difference therebetween was36° C. The expansion ratio was 11.3 times at 230° C.

Example 22

Suspension polymerization was performed in the same manner with Example15 except adding, in addition to 108 g of methacrylonitrile and 92 g ofmethacrylic acid, 1.0 g of trimethylolpropanetrimethacrylate to therebyobtain a thermally foamable microsphere with an average particlediameter of 31 μm. The blending proportion oftrimethylolpropanetrimethacrylate in the polymerizable monomer mixtureof Example 22 was 0.11 mol %.

The TMA measurement was performed using, as a sample, the thermallyfoamable microsphere obtained as a result of the above manner as it was.As a result, the expanding starting temperature was 185° C., the maximumexpansion temperature was 220° C., and the difference therebetween was35° C. The expansion ratio was 8.0 times at 230° C.

Example 23

Suspension polymerization was performed in the same manner with Example15 except adding 98 g of methacrylonitrile, 92 g of methacrylic acid,and 10 g of methyl acrylate (indicated as MA in Tables) to therebyobtain a thermally foamable microsphere with an average particlediameter of 27 μm. The molar ratio of methacrylonitrile to methacrylicacid was 1.4:1 and the blending proportion of methyl acrylate was 5% byweight in Example 23.

The TMA measurement was performed using, as a sample, the thermallyfoamable microsphere obtained as a result of the above manner as it was.As a result, the expanding starting temperature was 189° C., the maximumexpansion temperature was 259° C., and the difference therebetween was70° C. The expansion ratio was 13.4 times at 230° C.

Example 24

Suspension polymerization was performed in the same manner with Example15 except adding 98 g of methacrylonitrile, 92 g of methacrylic acid,and 10 g of methyl methacrylate (indicated as MMA in Tables) to therebyobtain a thermally foamable microsphere with an average particlediameter of 25 μm. The molar ratio of methacrylonitrile to methacrylicacid was 1.4:1 and the blending proportion of methyl acrylate was 5% byweight in Example 24.

The TMA measurement was performed using, as a sample, the thermallyfoamable microsphere obtained as a result of the above manner as it was.As a result, the expanding starting temperature was 185° C., the maximumexpansion temperature was 242° C., and the difference therebetween was57° C. The expansion ratio was 14.2 times at 230° C.

Example 25

Suspension polymerization was performed in the same manner with Example15 except adding 88 g of methacrylonitrile, 92 g of methacrylic acid,and 20 g of methyl methacrylate to thereby obtain a thermally foamablemicrosphere with an average particle diameter of 27 μm. The molar ratioof methacrylonitrile to methacrylic acid was 1.2:1 and the blendingproportion of methyl acrylate was 10% by weight in Example 25.

The TMA measurement was performed using, as a sample, the thermallyfoamable microsphere obtained as a result of the above manner as it was.As a result, the expanding starting temperature was 186° C., the maximumexpansion temperature was 235° C., and the difference therebetween was49° C. The expansion ratio was 13.3 times at 230° C.

Example 26

Suspension polymerization was performed in the same manner with Example15 except adding 104 g of methacrylonitrile, 92 g of methacrylic acid,and 4 g of dimethylamino ethyl methacrylate (indicated as DMAEMA inTables) to thereby obtain a thermally foamable microsphere with anaverage particle diameter of 24 μm. The molar ratio of methacrylonitrileto methacrylic acid was 1.5:1 and the blending proportion ofdimethylamino ethyl methacrylate was 2% by weight in Example 26.

The TMA measurement was performed using, as a sample, the thermallyfoamable microsphere obtained as a result of the above manner as it was.As a result, the expanding starting temperature was 190° C., the maximumexpansion temperature was 251° C., and the difference therebetween was61° C. The expansion ratio was 11.4 times at 230° C.

TABLE 1 b* Value Average Expanding Maximum (Yellowness) Particlestarting expansion Expansion after Heated Blending Composition ofDiameter temperature temperature ratio at 240° C. for PolymerizableMixture Foaming Agent (μm) ° C. ° C. (times) 2 minutes Initiator Ex. 1MAN 88 g Molar Ratio Isooctane 60 g 40 Non Non 8.4 *1 24.5 V-60 MAA 112g 1:1 Heat-Treated Heat-Treated 2 g 195 217 After Heated After Heated at170° C. for at 170° C. for 2 minutes 2 minutes 195 217 Ex. 2 MAN 110 gMolar Ratio 39 186 214 8.4 *1 26.8 MAA 90 g 1.6:1 Ex. 3 MAN 132 g MolarRatio 41 171 255 10.5 *2 27.1 MAA 68 g 2.5:1 Ex. 4 MAN 154 g Molar Ratio50 180 260 8.6 *2 35.4 MAA 46 g 4.3:1 Ex. 5 MAN 88 g Molar RatioIsopentane 60 g 40 185 240 4.5 *1 25 MAA 112 g 1:1 Ex. 6 MAN 110 g MolarRatio 49 170 240 9.1 *2 27 MAA 90 g 1.6:1 Ex. 7 MAN 132 g Molar Ratio 47155 220 19.2 *3 27.5 MAA 68 g 2.5:1 Ex. 8 MAN 154 g Molar Ratio 50 130210 17.3 *4 36 MAA 46 g 4.3:1 Ex. 9 MAN 132 g Molar Ratio Isododecane 60g 31 251 279 1.5 *1 28 MAA 68 g 2.5:1 Ex. 10 MAN 130 g Molar RatioIsooctane 60 g 34 171 245 10.0 *2 27 MAA 66 g 2.5:1 MA 4 g Ex. 11 MAN130 g Molar Ratio Isopentane 60 g 50 150 220 19.1 *3 26.9 MAA 66 g 2.5:1MA 4 g Ex. 13 MAN 175 g Molar Ratio Isooctane 60 g 27 211 218 6.5 *2 41MAA 25 g 9:1 Ex. 14 MAN 129 g Molar Ratio 27 204 259 17.0 *1 31 MAA 71 g2.3:1 Ex. 15 MAN 108 g Molar Ratio 26 189 266 17.6 *1 27 MAA 92 g 1.5:1Ex. 16 MAN 88 g Molar Ratio 31 Non Non 14.5 *1 24 MAA 112 g 1:1Heat-Treated Heat-Treated 199 263 After Heated After Heated at 180° C.for at 180° C. for 10 minutes 10 minutes 197 266 Ex. 17 MAN 88 g MolarRatio 30 200 250 7.1 *1 23 LPO MAA 112 g 1:1 3 g Ex. 18 MAN 68 g MolarRatio 28 207 232 4.1 *1 23 MAA 132 g 0.7:1 Ex. 19 MAN 175 g Molar Ratio30 213 218 6.7 *1 V-60 MAA 25 g 9:1 2 g TMPTMA 0.4 g 0.04 mol % Ex. 20MAN 108 g Molar Ratio 26 188 250 10.6 *1 MAA 92 g 1.5:1 TMPTMA 0.2 g0.02 mol % Ex. 21 MAN 108 g Molar Ratio 29 187 223 11.3 *1 MAA 92 g1.5:1 TMPTMA 0.6 g 0.07 mol % Ex. 22 MAN 108 g Molar Ratio 31 185 2208.0 *1 MAA 92 g 1.5:1 TMPTMA 1.0 g 0.11 mol % Ex. 23 MAN 98 g MolarRatio 27 189 259 13.4 *1 MAA 92 g 1.4:1 MA 10 g 5 parts Ex. 24 MAN 98 gMolar Ratio 25 185 242 14.2 *1 MAA 92 g 1.4:1 MMA 10 g 5 parts Ex. 25MAN 88 g Molar Ratio 27 186 235 13.3 *1 MAA 92 g 1.2:1 MMA 20 g 10 partsEx. 26 MAN 104 g Molar Ratio 24 190 251 11.4 *1 MAA 92 g 1.5:1 DMAEMA 4g 2 parts *1: 230° C., *2: 220° C., *3: 210° C., *4: 200° C., *5: 190°C.

Example 27

Suspension polymerization was performed in the same manner with Example15 except using 60 g of isododecane in place of 60 g of isooctane as thefoaming agent to thereby obtain a thermally foamable microsphere with anaverage particle diameter of 26 μm (See Table 2).

The TMA measurement was performed using, as a sample, the thermallyfoamable microsphere obtained as a result of the above manner as it was.As a result, the expanding starting temperature was 232° C., the maximumexpansion temperature was 283° C., and the difference therebetween was51° C. The heat foamed particle density was 0.0612 at 240° C. and 0.0236at 250° C. (see Table 2).

Example 28

Suspension polymerization was performed in the same manner with Example15 except using 60 g of isopentane in place of 60 g of isooctane as thefoaming agent to thereby obtain a thermally foamable microsphere with anaverage particle diameter of 31 μm.

The TMA measurement was performed using, as a sample, the thermallyfoamable microsphere obtained as a result of the above manner as it was.As a result, the expanding starting temperature was 168° C., the maximumexpansion temperature was 234° C., and the difference therebetween was66° C. The expansion ratio was 14.4 times at 230° C. The heat foamedparticle density was 0.0116 at 220° C., 0.0072 at 230° C., and 0.0061 at240° C.

Example 29

Suspension polymerization was performed in the same manner with Example15 except using 40 g of isobutane in place of 60 g of isooctane as thefoaming agent to thereby obtain a thermally foamable microsphere with anaverage particle diameter of 27 μm.

The TMA measurement was performed using, as a sample, the thermallyfoamable microsphere obtained as a result of the above manner as it was.As a result, the expanding starting temperature was 159° C., the maximumexpansion temperature was 228° C., and the difference therebetween was69° C. The expansion ratio was 9.8 times at 230° C. The heat foamedparticle density was 0.0108 at 220° C., 0.0104 at 230° C., and 0.0146 at240° C.

Example 30

Suspension polymerization was performed in the same manner with Example15 except using 20 g of isobutane and 40 g of isododecane in place of 60g of isooctane as the foaming agent to thereby obtain a thermallyfoamable microsphere with an average particle diameter of 26 μm.

The TMA measurement was performed using, as a sample, the thermallyfoamable microsphere obtained as a result of the above manner as it was.As a result, the expanding starting temperature was 175° C., the maximumexpansion temperature was 240° C., and the difference therebetween was65° C. The expansion ratio was 10.3 times at 230° C. The heat foamedparticle density was 0.0097 at 230° C., 0.0108 at 240° C., and 0.0120 at250° C.

Example 31

Suspension polymerization was performed in the same manner with Example15 except using 10 g of isobutane and 50 g of isododecane in place of 60g of isooctane as the foaming agent to thereby obtain a thermallyfoamable microsphere with an average particle diameter of 26 μm.

The TMA measurement was performed using, as a sample, the thermallyfoamable microsphere obtained as a result of the above manner as it was.As a result, the expanding starting temperature was 198° C., the maximumexpansion temperature was 260° C., and the difference therebetween was62° C. The expansion ratio was 8.7 times at 230° C. The heat foamedparticle density was 0.0123 at 230° C., 0.0113 at 240° C., and 0.0119 at250° C.

Example 32

Suspension polymerization was performed in the same manner with Example15 except using 5 g of isobutane and 55 g of isododecane in place of 60g of isooctane as the foaming agent to thereby obtain a thermallyfoamable microsphere with an average particle diameter of 25 μm.

The TMA measurement was performed using, as a sample, the thermallyfoamable microsphere obtained as a result of the above manner as it was.As a result, the expanding starting temperature was 200° C., the maximumexpansion temperature was 277° C., and the difference therebetween was77° C. The expansion ratio was 5.8 times at 230° C. The heat foamedparticle density was 0.0221 at 230° C., 0.0205 at 240° C., and 0.0140 at250° C.

Example 33

Suspension polymerization was performed in the same manner with Example15 except using 20 g of isopentane and 40 g of isododecane in place of60 g of isooctane as the foaming agent to thereby obtain a thermallyfoamable microsphere with an average particle diameter of 25 μm.

The TMA measurement was performed using, as a sample, the thermallyfoamable microsphere obtained as a result of the above manner as it was.As a result, the expanding starting temperature was 193° C., the maximumexpansion temperature was 237° C., and the difference therebetween was44° C. The expansion ratio was 11.8 times at 230° C. The heat foamedparticle density was 0.0080 at 230° C. and 0.0088 at 240° C.

Example 34

Suspension polymerization was performed in the same manner with Example15 except using 10 g of isopentane and 50 g of isododecane in place of60 g of isooctane as the foaming agent to thereby obtain a thermallyfoamable microsphere with an average particle diameter of 24 μm.

The TMA measurement was performed using, as a sample, the thermallyfoamable microsphere obtained as a result of the above manner as it was.As a result, the expanding starting temperature was 195° C., the maximumexpansion temperature was 264° C., and the difference therebetween was69° C. The expansion ratio was 8.5 times at 230° C. The heat foamedparticle density was 0.0127 at 230° C., 0.0117 at 240° C., and 0.0110 at250° C.

Example 35

Suspension polymerization was performed in the same manner with Example15 except using 5 g of isopentane and 55 g of isododecane in place of 60g of isooctane as the foaming agent to thereby obtain a thermallyfoamable microsphere with an average particle diameter of 22 μm.

The TMA measurement was performed using, as a sample, the thermallyfoamable microsphere obtained as a result of the above manner as it was.As a result, the expanding starting temperature was 208° C., the maximumexpansion temperature was 272° C., and the difference therebetween was64° C. The heat foamed particle density was 0.0155 at 240° C. and 0.0154at 250° C.

Example 36

Suspension polymerization was performed in the same manner with Example15 except using 40 g of isooctane in place of 60 g of isooctane as thefoaming agent to thereby obtain a thermally foamable microsphere with anaverage particle diameter of 25 μm.

The TMA measurement was performed using, as a sample, the thermallyfoamable microsphere obtained as a result of the above manner as it was.As a result, the expanding starting temperature was 188° C., the maximumexpansion temperature was 256° C., and the difference therebetween was68° C. The expansion ratio was 8.6 times at 230° C. The heat foamedparticle density was 0.0125 at 230° C., 0.0116 at 240° C., and 0.0124 at250° C.

Example 37

Suspension polymerization was performed in the same manner with Example15 except using 80 g of isooctane in place of 60 g of isooctane as thefoaming agent to thereby obtain a thermally foamable microsphere with anaverage particle diameter of 27 μm.

The TMA measurement was performed using, as a sample, the thermallyfoamable microsphere obtained as a result of the above manner as it was.As a result, the expanding starting temperature was 187° C., the maximumexpansion temperature was 260° C., and the difference therebetween was73° C. The expansion ratio was 12.4 times at 230° C. The heat foamedparticle density was 0.0075 at 230° C., 0.0069 at 240° C., and 0.0068 at250° C.

Example 38

Suspension polymerization was performed in the same manner with Example15 except using 100 g of isooctane in place of 60 g of isooctane as thefoaming agent to thereby obtain a thermally foamable microsphere with anaverage particle diameter of 23 μm.

The TMA measurement was performed using, as a sample, the thermallyfoamable microsphere obtained as a result of the above manner as it was.As a result, the expanding starting temperature was 187° C., the maximumexpansion temperature was 260° C., and the difference therebetween was73° C. The expansion ratio was 12.8 times at 230° C. The heat foamedparticle density was 0.0072 at 230° C., 0.0061 at 240° C., and 0.0068 at250° C.

Example 39

Suspension polymerization was performed in the same manner with Example15 except adding 110 g of methacrylonitrile, 86 g of methacrylic acid,and 4 g of methyl acrylate, and further adding 22 g of isopentane and 22g of isooctane in place of 60 g of isooctane as the foaming agent tothereby obtain a thermally foamable microsphere with an average particlediameter of 21 μm.

The TMA measurement was performed using, as a sample, the thermallyfoamable microsphere obtained as a result of the above manner as it was.As a result, the expanding starting temperature was 176° C., the maximumexpansion temperature was 231° C., and the difference therebetween was55° C. The expansion ratio was 11.0 times at 230° C. The heat foamedparticle density was 0.0106 at 210° C., 0.0089 at 220° C., and 0.0094 at230° C.

Example 40

Suspension polymerization was performed in the same manner with Example15 except adding 110 g of methacrylonitrile, 86 g of methacrylic acid,and 4 g of methyl acrylate, and further adding 30 g of isopentane and 30g of isooctane in place of 60 g of isooctane as the foaming agent tothereby obtain a thermally foamable microsphere with an average particlediameter of 24 μm.

The TMA measurement was performed using, as a sample, the thermallyfoamable microsphere obtained as a result of the above manner as it was.As a result, the expanding starting temperature was 175° C., the maximumexpansion temperature was 235° C., and the difference therebetween was60° C. The expansion ratio was 14.2 times at 220° C. The heat foamedparticle density was 0.0093 at 210° C., 0.0062 at 220° C., and 0.0068 at230° C.

Example 41

Suspension polymerization was performed in the same manner with Example15 except adding 110 g of methacrylonitrile, 86 g of methacrylic acid,and 4 g of methyl acrylate, and further adding 40 g of isopentane and 40g of isooctane in place of 60 g of isooctane as the foaming agent tothereby obtain a thermally foamable microsphere with an average particlediameter of 26 μm.

The TMA measurement was performed using, as a sample, the thermallyfoamable microsphere obtained as a result of the above manner as it was.As a result, the expanding starting temperature was 172° C., the maximumexpansion temperature was 241° C., and the difference therebetween was69° C. The expansion ratio was 16.0 times at 210° C. The heat foamedparticle density was 0.0083 at 210° C., 0.0054 at 220° C., and 0.0052 at230° C.

Example 42

Suspension polymerization was performed in the same manner with Example15 except adding 110 g of methacrylonitrile, 86 g of methacrylic acid,and 4 g of methyl acrylate, and further adding 50 g of isopentane and 50g of isooctane in place of 60 g of isooctane as the foaming agent tothereby obtain a thermally foamable microsphere with an average particlediameter of 30 μm.

The TMA measurement was performed using, as a sample, the thermallyfoamable microsphere obtained as a result of the above manner as it was.As a result, the expanding starting temperature was 168° C., the maximumexpansion temperature was 247° C., and the difference therebetween was79° C. The expansion ratio was 18.2 times at 210° C. The heat foamedparticle density was 0.0083 at 210° C., 0.0044 at 220° C., and 0.0047 at230° C.

TABLE 2 Average Expanding Maximum Particle starting expansion ExpansionFoamed Blending Composition of Diameter temperature temperature ratioParticle Polymerizable Mixture Foaming Agent (μm) ° C. ° C. (times)Density Initiator Ex. 15 MAN 108 g Molar Ratio Isooctane 60 g 26 189 26617.6 *1 230° C.: 0.0046 V-60 MAA 92 g 1.5:1 240° C.: 0.0045 2 g 250° C.:0.0068 Ex. 27 Isododecane 60 g 23 232 283 Non *1 230° C.: Non FoamedFoamed 240° C.: 0.0612 250° C.: 0.0236 Ex. 28 Isopentane 60 g 31 168 23414.4 *1 220° C.: 0.0116 230° C.: 0.0072 240° C.: 0.0061 Ex. 29 Isobutane40 g 27 159 228 9.8 *1 220° C.: 0.0108 230° C.: 0.0104 240° C.: 0.0146Ex. 30 Isobutane 20 g 26 175 240 10.3 *1 230° C.: 0.0097 Isododecane 40g 240° C.: 0.0108 250° C.: 0.0120 Ex. 31 Isobutane 10 g 26 198 260 8.7*1 230° C.: 0.0123 Isododecane 50 g 240° C.: 0.0113 250° C.: 0.0119 Ex.32 Isobutane 5 g 25 200 277 5.8 *1 230° C.: 0.0221 Isododecane 55 g 240°C.: 0.0205 250° C.: 0.0140 Ex. 33 Isopentane 20 g 25 193 237 11.8 *1230° C.: 0.0080 Isododecane 40 g 240° C.: 0.0088 250° C.: — Ex. 34Isopentane 10 g 24 195 264 8.5 *1 230° C.: 0.0127 Isododecane 50 g 240°C.: 0.0117 250° C.: 0.0110 Ex. 35 Isopentane 5 g 22 208 272 — *1 230°C.: — Isododecane 55 g 240° C.: 0.0155 250° C.: 0.0154 Ex. 36 Isooctane40 g 25 188 256 8.6 *1 230° C.: 0.0125 240° C.: 0.0116 250° C.: 0.0124Ex. 37 Isooctane 80 g 27 187 260 12.4 *1 230° C.: 0.0075 240° C.: 0.0069250° C.: 0.0068 Ex. 38 Isooctane 100 g 23 187 260 12.8 *1 230° C.:0.0072 240° C.: 0.0061 250° C.: 0.0068 Ex. 39 MAN 110 g Molar RatioIsopentane 22 g 21 176 231 11.0 *1 210° C.: 0.0106 MAA 86 g 1.6:1Isooctane 22 g 220° C.: 0.0089 MA 4 g 230° C.: 0.0094 Ex. 40 Isopentane30 g 24 175 235 14.2 *2 210° C.: 0.0093 Isooctane 30 g 220° C.: 0.0062230° C.: 0.0068 Ex. 41 Isopentane 40 g 26 172 241 16.0 *3 210° C.:0.0083 Isooctane 40 g 220° C.: 0.0054 230° C.: 0.0052 Ex. 42 Isopentane50 g 30 168 247 18.2 *3 210° C.: 0.0083 Isooctane 50 g 220° C.: 0.0044230° C.: 0.0047 *1: 230° C., *2: 220° C., *3: 210° C., *4: 200° C., *5:190° C.

Example 43

Suspension polymerization was performed in the same manner with Example15 except using 50 g of 20% by weight colloidal silica in place of 65 gof 20% by weight colloidal silica and adjusting the number of rotationof an emulsifier to 8,500 r/m in preparation of an aqueous dispersionmedium to thereby obtain a thermally foamable microsphere with anaverage particle diameter of 39 μm (see Table 3).

The TMA measurement was performed using, as a sample, the thermallyfoamable microsphere obtained as a result of the above manner as it was.As a result, the expanding starting temperature was 185° C., the maximumexpansion temperature was 266° C., and the difference therebetween was81° C. The expansion ratio was 11.3 times at 230° C. The heat foamedparticle density was 0.0210 at 210° C., 0.0113 at 220° C., and 0.0085 at230° C. (see Table 3).

Example 44

Suspension polymerization was performed in the same manner with Example15 except using 40 g of 20% by weight colloidal silica in place of 65 gof 20% by weight colloidal silica and adjusting the number of rotationof an emulsifier to 7,500 r/m in preparation of an aqueous dispersionmedium to thereby obtain a thermally foamable microsphere with anaverage particle diameter of 58 μm.

The TMA measurement was performed using, as a sample, the thermallyfoamable microsphere obtained as a result of the above manner as it was.As a result, the expanding starting temperature was 181° C., the maximumexpansion temperature was 232° C., and the difference therebetween was51° C. The expansion ratio was 11.3 times at 230° C. The heat foamedparticle density was 0.0150 at 210° C., 0.0100 at 220° C., and 0.0086 at230° C.

Example 45

Suspension polymerization was performed in the same manner with Example15 except using 20 g of 20% by weight colloidal silica in place of 65 gof 20% by weight colloidal silica and adjusting the number of rotationof an emulsifier to 5,500 r/m in preparation of an aqueous dispersionmedium to thereby obtain a thermally foamable microsphere with anaverage particle diameter of 118 μm.

The TMA measurement was performed using, as a sample, the thermallyfoamable microsphere obtained as a result of the above manner as it was.As a result, the expanding starting temperature was 177° C., the maximumexpansion temperature was 201° C., and the difference therebetween was24° C. The expansion ratio was 2.8 times at 210° C. The heat foamedparticle density was 0.0598 at 210° C., 0.0641 at 220° C., and 0.0748 at230° C.

TABLE 3 Number of Average Expanding Maximum Rotation Particle startingexpansion Expansion Foamed Blending Composition of Colloidal of Diametertemperature temperature ratio Particle Polymerizable Mixture SilicaEmulsifier (μm) ° C. ° C. (times) Density Initiator Ex. 15 MAN 108 gMolar Ratio 65 g 9500 r/m 26 189 266 17.6 *1 210° C.: 0.0201 V-60 g MAA92 g 1.5:1 220° C.: 0.0074 Isooctane 60 g 230° C.: 0.0046 Ex. 43 50 g8500 r/m 39 185 266 11.3 *1 210° C.: 0.0210 220° C.: 0.0113 230° C.:0.0085 Ex. 44 40 g 7500 r/m 58 181 232 11.3 *1 210° C.: 0.0150 220° C.:0.0100 230° C.: 0.0086 Ex. 45 20 g 5500 r/m 118 177 201 2.8 *3 210° C.:0.0598 220° C.: 0.0641 230° C.: 0.0748 *1: 230° C., *2: 220° C., *3:210° C., *4: 200° C., *5: 190° C.

Comparative-Example 1

Comparative Example 1 is a test for confirming influences caused by theuse of a large amount of acrylonitrile. Suspension polymerization wasperformed in the same manner with Example 1 except using 45.4 g ofacrylonitrile, 45.4 g of methacrylonitrile, and 109.2 g of methacrylicacid in place of 88 g of methacrylonitrile and 112 g of methacrylicacid. As a result, the polymer agglomerated in the middle ofpolymerization, and thus a normal thermally foamable microsphere was notsuccessfully obtained (see Table 4).

Comparative Example 2

In order to confirm the particle formability of a polymerizable mixturewhose composition is similar to that of Examples of Patent Document 2,suspension polymerization was performed in the same manner with Example1 except using 45.4 g of acrylonitrile, 45.4 g of methacrylonitrile, and109.2 g of methacrylic acid in place of 88 g of methacrylonitrile and112 g of methacrylic acid, and further adding 2.72 g of ethylene glycoldimethacrylate (indicated as EGDMA in Table) as a cross linkablemonomer. As a result, the polymer agglomerated in the middle ofpolymerization, and thus a normal thermally foamable microsphere was notsuccessfully obtained.

Comparative Example 3

In order to confirm influences caused by the use of a larger amount ofacrylonitrile, suspension polymerization was performed in the samemanner with Example 1 except using 66.6 g of acrylonitrile, 66.6 g ofmethacrylonitrile, and 66.6 g of methacrylic acid in place of 88 g ofmethacrylonitrile and 112 g of methacrylic acid. As a result, thepolymer agglomerated in the middle of polymerization, and thus a normalthermally foamable microsphere was not successfully obtained.

Comparative Example 4

In order to confirm the particle formability of a polymerizable mixturewhose composition is similar to that of Examples of Patent Document 2,suspension polymerization was performed in the same manner with Example1 except using 66.6 g of acrylonitrile, 66.6 g of methacrylonitrile, and66.6 g of methacrylic acid in place of 88 g of methacrylonitrile and 112g of methacrylic acid, and further adding 2.86 g of ethylene glycoldimethacrylate as a cross linkable monomer.

As a result, the polymer agglomerated in the middle of polymerization,and thus a normal thermally foamable microsphere was not successfullyobtained.

Comparative Example 5

Suspension polymerization was performed in the same manner with Example1 except using only 200 g of methacrylic acid in place of 88 g ofmethacrylonitrile and 112 g of methacrylic acid. As a result, thepolymer agglomerated in the middle of polymerization.

Comparative Example 6

Suspension polymerization was performed in the same manner with Example1 except using only 200 g of methacrylonitrile in place of 88 g ofmethacrylonitrile and 112 g of methacrylic acid to thereby obtain athermally foamable microsphere with an average particle diameter of 47μm. The resulted microsphere did not foam. The b* value was 200.

Comparative Example 7

In order to confirm influences of a cross-linkable monomer, suspensionpolymerization was performed in the same manner with Example 3 exceptadding 2.72 g of ethylene glycol dimethacrylate as a cross-linkablemonomer to thereby obtain a thermally foamable microsphere with anaverage particle diameter of 50 μm. The addition amount of thecross-linkable monomer was 0.5 mol % relative to the polymerizablemonomer.

The TMA measurement was performed using, as a sample, the thermallyfoamable microsphere obtained as a result of the above manner as it was.As a result, the expanding starting temperature was 169° C., the maximumexpansion temperature was 173° C. The expansion ratio was sharplylowered to be 1.1 times at 220° C.

Comparative Example 8

Comparative Example 8 is a test for confirming influences on the foamingbehavior. Suspension polymerization was performed in the same mannerwith Example 1 except using 67 g of acrylonitrile, 31 g ofmethacrylonitrile, 2 g of methacrylic acid, and 1.5 g ofdiethyleneglycol dimethacrylate (indicated as DEGDMA in Table) in placeof 88 g of methacrylonitrile and 112 g of methacrylic acid, and using 1g of isopentane, 13 g of isooctane, and 16 g of isododecane in place of60 g of isooctane as the foaming agent to thereby obtain a thermallyfoamable microsphere with an average particle diameter of 49 μm. Theaddition amount of the cross-linkable monomer was 0.35 mol % relative tothe polymerizable monomer.

The TMA measurement was performed using, as a sample, the thermallyfoamable microsphere obtained as a result of the above manner as it was.As a result, the expanding starting temperature was 204° C., the maximumexpansion temperature was 209° C., and the difference therebetween was5° C. The above-mentioned thermally foamable microsphere was heated at170° C. for 2 minutes, and then the TMA measurement was performed. Theexpanding starting temperature was 135° C. and the maximum expansiontemperature was 194° C. The expansion ratio after heated at 170° C. for2 minutes was 8.3 times at 1900C.

FIG. 2 shows changes (foaming behavior) in the foaming degree between atthe expanding starting temperature and at the maximum expansiontemperature at the time of TMA measurement. It is revealed that thethermally foamable microsphere obtained in Comparative Example 8 isreduced in both the expanding starting temperature and the maximumexpansion temperature when not heated and when heated at 170° C. for 2minutes, and moreover the foaming behavior between at the expandingstarting temperature and at the maximum expansion temperature sharplychanges (also see FIG. 1).

TABLE 4 b* Value (Yellowness) Average Expanding Maximum after Particlestarting expansion Expansion Heated at Blending Composition of Diametertemperature temperature ratio 240 for 2 Polymerizable Mixture FoamingAgent (μm) ° C. ° C. (times) minutes Comparative AN 45.4 g Molar RatioIsooctane 60 g Normal Thermally Foamable microsphere is not Obtained Ex.1 MAN 45.4 g 0.5:1 (Formed into a Polymer Lump in the middle ofPolymerization). MAA 109.2 g 0.00 mol % EGDMA 0 g Comparative AN 45.4 gMolar Ratio Normal Thermally Foamable microsphere is not Obtained Ex. 2MAN 45.4 g 0.5:1 (Formed into a Polymer Lump in the middle ofPolymerization). MAA 109.2 g 0.49 mol % EGDMA 2.72 g Comparative AN 66.6g Molar Ratio Normal Thermally Foamable microsphere is not Obtained Ex.3 MAN 66.6 g 1.3:1 (Formed into a Polymer Lump in the middle ofPolymerization). MAA 66.6 g 0.00 mol % EGDMA 0 g Comparative AN 66.6 gMolar Ratio Normal Thermally Foamable microsphere is not Obtained Ex. 4MAN 66.6 g 1.3:1 (Formed into a Polymer Lump in the middle ofPolymerization). MAA 66.6 g 0.48 mol % EGDMA 2.86 g Comparative MAA 200g 0:1 Normal Thermally Foaming Microcapsule is not Obtained Ex. 5(Formed into a Polymer Lump in the middle of Polymerization).Comparative MAN 200 g 1:0 47 Not Foamed. 200 Ex. 6 Comparative MAN 132 gMolar Ratio 50 169 173 1.1 *2 Ex. 7 MAA 68 g 2.5:1 EGDMA 2.72 g 0.50 mol% Comparative AN 67 g 0.35 mol % Isopentane 1 g 49 Non Non Non *5 Ex. 8MAN 31 g Isooctane 13 g Heat-Treated Heat-Treated Foamed MMA 2 gIsododecane 16 g 204 209 DEGDMA 1.5 g After Heated After Heated 8.3 *5at 170° C. for at 170° C. for 2 minutes 2 minutes 135 194 *1: 230° C.,*2: 220° C., *3: 210° C., *4: 200° C., *5: 190° C.

As is clear from the results shown in “Table 1” above, in each Exampleof the thermally foamable microsphere of the present invention, thedifference of the expanding starting temperature and the maximumexpansion temperature was large. More specifically, the differences ofthe expanding starting temperature and the maximum expansion temperaturein each Example were as follows: Example 1: 22° C., Example 2: 28° C.,Example 3: 84° C., Example 4: 80° C., Example 5: 55° C., Example 6: 70°C., Example 7: 65° C., Example 8: 80° C., Example 9: 28° C., Example 10:74° C., and Example 11: 70° C. This clarifies that the thermallyfoamable microsphere of the present invention is excellent in the heatresistance.

Moreover, each Example of the thermally foamable microsphere of thepresent invention has a high expansion ratio. In addition, as shown inExamples 1 and 16, even after heat treated, the expanding startingtemperature did not lower, the foaming behavior did not change, and astable formability was maintained (see Tables 1 and 2, and FIG. 1).

Furthermore, the thermally foamable microsphere of the present inventionshowed less yellowing at the time of heating. Moreover, in each Example,aggregation did not occur in the middle of polymerization, and thus thethermally foamable microsphere was successfully produced stably.

In contrast, in Comparative Examples 1 and 2 of the monomer mixture inwhich acrylonitrile was added to methacrylonitrile and methacrylic acid,the mixture was formed into a polymer lump in the middle ofpolymerization, and thus a normal thermally foamable microsphere was notobtained (see Table 4). Moreover, in Comparative Example 7 in whichethylene glycol dimethacrylate as a cross-linkable monomer was added,the difference between the expanding starting temperature and themaximum expansion temperature was as small as about 4° C. and theexpansion ratio also sharply decreased at 220° C. (see Table 4).

Furthermore, in Comparative Example 8, the expanding startingtemperature noticeably decreased when the thermally foamable microspherewas not heated and after the thermally foamable microsphere was heatedat 170° C. for 2 minutes, and then the foaming behavior sharply changed(see Table 4 and FIG. 2).

INDUSTRIAL APPLICABILITY

The present invention can be used as a technique of producing athermally foamable microsphere which is excellent in heat resistance andhas a high expansion ratio. Making good use of its expandability, thethermally foamable microsphere of the present invention is used as afiller for a paint for automobiles and the like, a foaming agent forwallpaper or foaming ink (for applying relief patterns to T-shirt andthe like), a shrink-preventing agents, etc. Moreover, utilizing thevolume increase property caused by the foaming, the thermally foamablemicrosphere of the present invention is used as an additive for thepurpose of reducing the weight of polymeric materials such as asynthetic resin (thermoplastic resin, thermosetting resin) and rubber, apaint and various materials making them porous and imparting variousfunctionalities. In particular, the present invention contributes toreducing the weight of interior members or tires of automobiles.Furthermore, the thermally foamable microsphere of the present inventioncan be suitably used for the fields of a paint, wallpaper, and ink,which are requiring surfaceness and smoothness. The thermally foamablemicrosphere of the present invention is excellent in processability, andtherefore can be suitably used for the fields requiring processing, suchas kneading, calendering, extruding, and injection molding.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a view illustrating changes (foaming behavior) in the degreeof expansion between at the expanding starting temperature and at themaximum expansion temperature of a thermally foamable microsphereaccording to Example 16.

FIG. 2 is a view illustrating changes (foaming behavior) in the degreeof expansion between at the expanding starting temperature and at themaximum expansion temperature of a thermally foamable microsphereaccording to Comparative Example 8.

FIG. 1

1. Foaming behavior before and after heat treatment (Example 16)2. Degree of expansion

3. Temperature (° C.)

4. Non heat-treatedAfter treated at 180° C. for 10 minutes

FIG. 2

1. Foaming behavior before and after heat treatment (Comparative Example8)2. Degree of expansion

3. Temperature (° C.)

4. Non heat-treatedAfter treated at 170° C. for 2 minutes

1. A thermally foamable microsphere, comprising: a foaming agent; and anouter shell encapsulating the foaming agent, the outer shell capable offorming a copolymer having a polymethacrylimide structure.
 2. Thethermally foamable microsphere according to claim 1, wherein monomersforming the polymethacrylimide structure by a copolymerization reactionare comprised of methacrylonitrile and methacrylic acid.
 3. Thethermally foamable microsphere according to claim 1, wherein a b* valueafter heated at 240° C. for 2 minutes is 100 or lower.
 4. The thermallyfoamable microsphere according to claim 1, wherein a variation in aexpanding starting temperature due to heat treatment at a temperaturelower than the expanding starting temperature is 7% or lower relative tothe expanding starting temperature before the heat treatment, and avariation in a maximum expansion temperature due to the heat treatmentis 7% or lower relative to the maximum expansion temperature before theheat treatment.
 5. A method of producing a thermally foamablemicrosphere in which a foaming agent is encapsulated in an outer shellcapable of forming a copolymer having a polymethacrylimide structure,the method comprising: performing suspension polymerization of a mixtureof monomers as main components comprised of a nitril monomer and monomerhaving a carboxyl group in the presence of the foaming agent in anaqueous dispersion medium containing a dispersion stabilizer.
 6. Theproduction method according to claim 5, wherein the nitril monomer ismethacrylonitrile and the monomer containing the carboxyl group ismethacrylic acid.
 7. The production method according to claim 6, whereinthe mixture of polymerizable monomer comprises at least: 70 to 100% byweight of a substance in which a molar ratio of methacrylonitrile tomethacrylic acid is 1:9 to 9:1; 0 to 30% by weight of vinyl monomercapable of copolymerizing with the substance; and to 0.4 mol % of across-linkable monomer of having 2 or more functionalities.
 8. Use ofthe thermally foamable microsphere as an additive comprising: a foamingagent; and an outer shell encapsulating the foaming agent, the outershell capable of forming a copolymer having a polymethacrylimidestructure, wherein monomers forming the polymethacrylimide structure bya copolymerization reaction are comprised of methacrylonitrile andmethacrylic acid or wherein a b* value after heated at 240° C. for 2minutes is 100 or lower, or wherein a variation in a expanding startingtemperature due to heat treatment at a temperature lower than theexpanding starting temperature is 7% or lower relative to the expandingstarting temperature before the heat treatment, and a variation in amaximum expansion temperature due to the heat treatment is 7% or lowerrelative to the maximum expansion temperature before the heat treatment.9. The thermally foamable microsphere according to claim 2, wherein a b*value after heated at 240° C. for 2 minutes is 100 or lower.
 10. Thethermally foamable microsphere according to claim 2, wherein a variationin a expanding starting temperature due to heat treatment at atemperature lower than the expanding starting temperature is 7% or lowerrelative to the expanding starting temperature before the heattreatment, and a variation in a maximum expansion temperature due to theheat treatment is 7% or lower relative to the maximum expansiontemperature before the heat treatment.
 11. The thermally foamablemicrosphere according to claim 3, wherein a variation in a expandingstarting temperature due to heat treatment at a temperature lower thanthe expanding starting temperature is 7% or lower relative to theexpanding starting temperature before the heat treatment, and avariation in a maximum expansion temperature due to the heat treatmentis 7% or lower relative to the maximum expansion temperature before theheat treatment.
 12. The thermally foamable microsphere according toclaim 9, wherein a variation in a expanding starting temperature due toheat treatment at a temperature lower than the expanding startingtemperature is 7% or lower relative to the expanding startingtemperature before the heat treatment, and a variation in a maximumexpansion temperature due to the heat treatment is 7% or lower relativeto the maximum expansion temperature before the heat treatment.